The field of the invention is excavator drive systems, and more particularly, means for reducing the transient loading on the mechanical portion of an excavator drive by compensating the response of the driving electrical system to sudden changes in loading.
Until recently mechanical means were used almost exclusively in the excavator field to suppress mechanical resonances and damp the shock of sudden changes in loading. For example, resilient cushions, dash pots and shock absorbers of various configurations were employed to reduce the peak transient loading on the mechanical elements of large shovels and dragline excavators caused by the impact of the bucket with rocks during rough digging. In addition to being quite costly, such devices add considerable weight and require continuous maintenance. Also, in the case of dragline excavators there are few effective mechanical means for reducing transient loading on the dragrope which connects directly to the bucket.
More recently, efforts have been made to reduce the effects of transient loading on the mechanical elements of an excavator drive system by compensating the driving electrical system. As disclosed in U.S. pat. No. 3,867,678 issued on Feb. 18, 1975 to Thomas A. Stoner and assigned to the Bucyrus-Erie Company, assignee of the present invention, such transient loading on the mechanical system is reflected into the driving electrical system as a sudden change in motor armature current, voltage or other operating parameter. By sensing such a change and developing an appropriate feedback signal for the motor drive control circuit, the loading on the driven mechanical elements can be significantly reduced during rough digging.